The present invention relates to thermoplastic drums and in particular to thermoplastic drums which can be grasped and lifted using available mechanical lifting apparatus.
Various types of lift apparatus have been utilized for lifting metal drums. For example, the parrotbeaker apparatus grasps the flange at a point around the upper top edge of a drum and thereafter tips the drum to one side supporting the bottom portion of the drum against a circular support surface. The drum is lifted by applying a lifting force at the grasping point. Similarly, a drum may be lifted utilizing a standard handtruck by tipping the drum, slipping a support shelf of the handtruck under the bottom of the drum and then positioning a hook-like finger over the edge of the annular peripheral rim of the drum to thereby tip the drum onto the handtruck.
Drums have also been lifted utilizing forklift or side-grabber apparatus. Such apparatus have tongs which fit around the side of the drum and underneath a suitable horizontal flange. The drum is then lifted by simply raising the tongs underneath the support flange so that a vertical force is applied to the support flange.
Still another type of lifting device is the chain hoist whereby hooks are positioned about the lip at each end of a steel drum with lifting effected by interconnecting the hooks with the chain and lifting the chain at a center location between the two ends of the drum.
With the advent of plastic drums, it has been necessary to devise specific structures to enable such drums to be lifted by one or more of the aforedescribed devices. However, special problems arise in the lifting of plastic drums because of the flexibility and resiliency of the plastic material out of which the drums are made. The present invention provides a thermoplastic drum apparatus which can be lifted by a parrotbeaker, a handtruck, a forklift, and a sidegrabber. In addition, in an optional configuration, the present invention enables the drum to be lifted utilizing a chain hoist apparatus.
Of course, it will be appreciated that the thermoplastic drums are flexible and resilient. Consequently, thermoplastic drums are subject to sidewall buckling if a heavy weight is placed on one side of the drum. This would result in the collapse of any drums stacked on the bottom drum. In order to minimize this problem, the present invention incorporates a grasping beak with a top edge defining an upper stacking ridge which is positioned vertically over the sidewall of the drum so that the weight of a drum placed on top of the stacking rim will be exerted substantially directly downward and thereby be supported by the sidewall of the lower drum with a minimum horizontal force component.
To further enable the drum sidewall to withstand buckling, it is preferred that at least the lower portion of the drum's sidewall be contoured radially inwardly between a center region of the drum and the bottom of the drum by a slight amount. This configuration will force most horizontal force components to be exerted radially outwardly on the drum making it more difficult to buckle the drum outwardly. Of course, a similarly contoured sidewall can also be provided between a center region of the drum and the top of the drum.
Finally, the rim member attached permanently and movably to the drum has a grasping beak. It will be appreciated that large drums capable of holding as much as 50 to 60 gallons will weigh as much as 750 to 800 pounds when full. Consequently, when a parrotbeaker or handtruck is used to lift the drum by grasping the rim member, tremendous stress is placed on the junction between the rim member and the drum. Hence, the necessity of an extremely strong attachment between the drum body and the rim member.
Various methods have been or can be used to make thermoplastic drums. For example, the drum may be injection-molded. Injection molding allows great detail to be incorporated while at the same time providing a rigid control over the specific configuration of features of the drum. Thus, a suitable grasping beak could be integrally molded as part of such a drum to provide the necessary strong bond. However, injection molding of the entire drum would be very expensive and therefore impractical.
Another method of molding is rotational molding whereby a mold is first made defining the external characteristics of the object to be molded. A powdered plastic is then placed in the mold and the mold rotated forcing the plastic into the particular cavities and contours of the mold under centrifugal force. The application of heat during this process melts the powder into a single molded piece. Making a suitable drum using this technique has several drawbacks, however. For example, rotational molding requires high-grade plastics which must be first ground into powder entailing additional cost. In addition, an integrally formed grasping beak will inherently have an inside concavity which allows the grasping beak to be somewhat flexible relative to the drum, thus increasing the difficulty with which the drum can be grasped and lifted. Hence, it is desird to fabricate a drum with a substantially solid grasping beak to increase the rigidity of the grasping beak relative to the drum.
The most economic means of forming a drum and the one which is most commonly used in making thermoplastic drums is the blow-molding process. However, the blow-molding process suffers from its inability to produce objects having sufficient detail. Hence, it is not possible to blow-mold a drum having an integrally formed grasping beak with a shape suitable for being grasped or otherwise used to lift the drum. Several methods have been previously devised for overcoming this problem. For example, applicant has previously used an injection-molded circular rim having a top and a side grasping flange which fits into a side and a top groove molded in the thermoplastic drum during the blow-molding process. The injection-molded ring is then snapped into place in the external molded grooves of the thermoplastic blow-molded drum. While this snap-on injection-molded ring provides a means by which the drum may be lifted utilizing the parrotbeaker, the handtruck, the forklift, or the sidegrabbers, it has been found that under certain conditions it is possible for the injection-molded ring to be pulled loose from the drum.
In another prior art device, a steel clamp ring is placed about the circumference of a blow-molded drum. However, it has been found that if the drum is dropped, the ring can pop off and be permanently bent because of the differences in the resilient characteristics of the ring and drum. Furthermore, if the drum is lifted by a parrotbeaker which grasps about the steel clamping ring, it is possible for the ring to be pulled from the drum.
In still another prior art device produced by Hedwin of New York, New York, one or more grasping beak members are injection-molded to obtain the necessary detail. The grasping beak members are then positioned at several different locations about the periphery of the drum mold. The grasping beak members are then heat-bonded to the blow-molded drum body during and as a consequence of blow-molding the heated thermoplastic utilized to form the drum against a smooth inwardly facing bonding surface of the injection-molded grasping beak members. The bonding surface, which is smooth and has a flat cross-sectional shape, is thereby bonded to the drum by the melting together of the grasping beak member and drum body.